The present invention relates to seals in a gas turbine for supplementing the chordal hinge seals between turbine nozzles and a turbine nozzle support ring and particularly relates to supplementary seals for substantially minimizing or eliminating leakage losses past the chordal hinge seals.
In a gas turbine, hot gases of combustion flow from combustors through first-stage nozzles and buckets and through the nozzles and buckets of follow-on turbine stages. The first-stage nozzles typically include an annular array or assemblage of cast nozzle segments each containing one or more nozzle stator vanes per segment. Each first-stage nozzle segment also includes inner and outer band portions spaced radially from one another. Upon assembly of the nozzle segments, the stator vanes are circumferentially spaced from one another to form an annular array thereof between annular inner and outer bands. A nozzle retaining ring coupled to the outer band of the first-stage nozzles supports the first-stage nozzles in the gas flow path of the turbine. An annular nozzle support ring, preferably split at a horizontal midline, is engaged by the inner band and supports the first-stage nozzles against axial movement.
In an exemplary arrangement, eighteen cast segments are provided with two vanes per segment. The annular array of segments are sealed one to the other along adjoining circumferential edges by side seals. The side seals seal between a high pressure region radially inwardly of the inner band, i.e., compressor discharge air at high pressure, and the hot gases of combustion in the hot gas flow path which are at a lower pressure.
Chordal hinge seals are used to seal between the inner band of the first-stage nozzles and an axially facing surface of the nozzle support ring. Each chordal hinge seal includes an axial projection which extends linearly along a chord line of the inner band portion of each nozzle segment. Particularly, the chordal hinge seal extends along an inner rail of each segment and which rail extends radially inwardly of the inner band portion. The chordal hinge seal projection lies in sealing engagement with the axially opposite facing sealing surface of the nozzle support ring.
During operation and/or repair of the first-stage nozzle, it has been found that warpage can leave gaps between the chordal hinge seals and the sealing surface of the nozzle support ring. These gaps enable leakage past the chordal hinge seals from the high pressure area radially within the annular inner band into the hot gas flow path. That is, the chordal hinge seals are inadequate to prevent leakage flow as the chordal hinge seal projections lose contact with the sealing surface of the nozzle support ring. Consequently, there is a need for a supplemental seal at the interface of the first-stage nozzles and nozzle support ring to minimize or eliminate the leakage flow past the chordal hinge seals.
In accordance with a preferred embodiment of the present invention, there is provided a supplemental seal between the first-stage nozzles and the nozzle support ring which eliminates or minimizes leakage past the chordal hinge seals and which is readily and easily installed. The supplemental seal hereof includes a composite, preferably tubular woven seal for sealing between the nozzle segments and the nozzle support ring. More particularly, the inner rail of each nozzle segment is provided with an arcuate cavity radially outwardly of the chordal hinge seal. The composite tubular woven seal is disposed in the cavity and bears against the annular sealing surface of the nozzle support ring. That is, when the chordal hinge engages the sealing surface of the nozzle support ring, the composite tubular woven seal is resiliently flattened between the first and second sealing surfaces of the nozzle support ring and the inner rail, respectively, to seal between those surfaces. Thus, in the event of axial warpage/deformation of the chordal hinge seal, the composite tubular woven seal expands to fill the gap.
The composite tubular woven supplemental seal is compliant as a result of the multiple layers forming the seal. The layers include an inner woven metal core, a fiber material, a metallic foil and a metal outer covering. Preferably, the inner metal core is formed of a woven stainless steel which is surrounded by a silica fiber. The fiber, in turn, is surrounded by a stainless steel metal foil and the outer covering is formed of a braided metal, for example, Haynes 188. Because of the nature of the composite tubular woven seal, the seal is compliant, particularly as a result of the resiliency of the metal core and surrounding silica fiber. Moreover, the metal foil layer surrounding the fiber prevents leakage between the supplemental seal and the sealing surface of the nozzle support ring, while the braided outer covering serves as a protective wear surface. The inner metal core and silica fibers retain the generally circular configuration of the supplemental seal in cross-section such that the seal, when compressed, is preloaded or biased for return to its circular cross-sectional configuration. In this manner, any leakage flow past the chordal hinge seal is sealed by the supplemental seal.
In a preferred embodiment according to the present invention, there is provided a turbine comprising a turbine nozzle support ring having a generally axially facing first surface, a turbine nozzle segment having at least one stator vane and including an inner band having a second surface in axial opposition to the first surface, a cavity in one support ring and a portion of the inner band of the segment, the cavity opening generally in an axial direction and toward another of the support ring and the inner band portion and a compliant seal in the cavity including a seal body formed of multiple layers of different materials for compliantly engaging against one of the first and second surfaces opposite the cavity to seal thereagainst.
In a further preferred embodiment according to the present invention, there is provided a gas turbine comprising a turbine nozzle support ring having a generally axially facing annular first surface, a plurality of turbine nozzle segments defining an annular array of stator vanes and an annular second surface in axial opposition to the first surface, each segment including an axially extending projection along a portion of the second surface for engagement with the first surface of the support ring to form a first seal therebetween for sealing between high and low pressure regions on opposite sides of the first seal, an annular cavity in one of the first and second surfaces radially outwardly of the first seal, the cavity opening generally in an axial direction and toward another of the first and second surfaces and a compliant seal in the cavity including a seal body formed of multiple layers of different materials for compliantly engaging against another of the first and second surfaces opposite the cavity to seal thereagainst.